Photochemical apparatus

ABSTRACT

A process for photo-oximating cycloalkanes by means of a gaseous nitrosating agent, in which the agent if fed into a radiation zone, without any cycloalkane present, the activated radicals are transferred immediately to an adjoining reaction zone containing the cycloalkane, and the oxime is provided in this reaction zone and drawn off. The radiation zone is separated from reaction zone by a perforated or gas-permeable partition, such as an electroformed grid made from a corrosion-resistant metal or alloy. Pressure is maintained in the radiation zone by means of a gas vehicle carrying the gaseous nitrosating agent, ensuring immediate transfer of the activated radicals and preventing any of the liquid phase in the radiation zone from leaking in.

iinited States Patent Lucas Mar. 26, 1974 Primary Examiner-Howard S.Williams [5 7] ABSTRACT A process for photo-oximating cycloalkanes bymeans of a gaseous nitrosating agent, in which the agent if fed into aradiation zone, without any cycloalkane present, the activated radicalsare transferred immediately to an adjoining reaction zone containing thecycloalkane, and the oxime is provided in this reaction zone and drawnoff.

The radiation zone is separated from reaction zone by a perforated orgas-permeable partition, such as an electroformed grid made from acorrosion-resistant metal or alloy.

Pressure is maintained in the radiation zone by means of a gas vehiclecarrying the gaseous nitrosating agent, ensuring immediate transfer ofthe activated radicals and preventing any of the liquid phase in theradiation zone from leaking in.

7 Claims, 3 Drawing Figures PATENTEMazs 1974 3.800 159 sum 1 OF 2PATENTEDNARZS m4 3.800.159

SHEET 2 BF 2 PHOTOCHEMIICAL APPARATUS Existing photochemical processesfor oximating cycloalkanes consist of exposing a mixture containing thecycloalkane, in liquid form or in solution, and the nitrosating agent inthe presence of excess hydrochloric acid, and possibly a carboxylicorganic acid, or inorganic acid, to the effect of photonic energyemitted by one or more doped or undoped high-pressure mercury lamps, oranother source of activation. These lamps are usually submerged in thereaction mixture, and it is found that, regardless of the proportions ofreagents, the wavelengths, the transparent, waterproof coatings appliedto the surfaces transmitting the light energy and in contact with thereaction mixture, or the method of extracting the reaction product, thereaction slows down considerably after a variable length of time,because of tarry deposits that form on the lamp covers. These depositsresult from the simultaneous presence of the light source, nitrosatingagent and cycloalkane inside the reactor.

Another drawback in existing processes is the need to remove excess heatoccurring in the reaction mixture, the optimum reaction temperaturebeing between and 30C.

This invention concerns a continuous cycloalkane oximation process thatovercomes these drawbacks, in which oximation is achieved by means of agaseous nitrosating agent fed into a radiation zone, without anycycloalkane present, the resulting dissociated activated particles ofthe agent being transferred immediately to an adjoining reaction zonecontaining the cycloalkane in liquid form, and from which the resultingoxime or oxime hydrochloride is drawn off.

The radiation zone is separated from the adjoining reaction zone by aperforated gas-permeable partition, and the nitrosating agent, mixedwith a gas vehicle, is fed in at sufficient pressure to ensure immediatetransfer of the active particles to the oximation zone, and prevent anytraces of cycloalkane from leaking into the radiation zone.

The process according to the invention can therefore be performedcontinuously, in two simultaneous stages, the first solelyphoto-chemical, to dissociate the nitrosating agent into activeparticles:

and the second chemical, involving the formation of a nitroso compoundand its isomerization into oxime:

-------s CDC=NOH A, Am 6 It is also unnecessary to cool the reactionmixture, since scission of the nitrosating agent molecule is unaffectedby heat. In addition, the gas circulating in the reaction zone cools thereaction mixture, as well as agitating it continually in a radialdirection, drawing the oxime away from the gas-permeable separatingpartition (which is thus not clogged by it).

The radiation zone therefore contains a gas phase, which filters anyharmful wavelengths, preventing them from passing through the permeablepartition into the oximation zone.

Finally, the quantic efficiency of the photolysis of a gaseousnitrosating agent, such as nitrosyl chloride, is much higher in the gasphase: 2 in the gas phase, and 0.75 in a carbon tetrachloride solution(cf. Symposium on photo-chemistry, 1957, Heidt, Livingstone, RabinowitchNew York, London, Wiley & Sons: The photolysis of nitrosyl chloride).Gas-phase photolysis allows far more active radicals to be liberatedthan in earlier processes.

The nitrosating agent generally belongs to the nitrosyl halides group,but a mixture of chlorine and nitrogen oxide can be used. It is fed intothe radiation zone at sufficient pressure to ensure immediate transferof the active particles, which, in the case of chlorine, have a life of6 X 10" seconds at 0.1 mm mercury pressure (cf. Sidgwick, The ChemicalElements,p. 1140-1955).

ITow eT/r, the Tire these ac tive particles raises no problem, sinceradicals with an average life of 8 X 10* seconds can be transportedwithout becoming deactivated over a distance of 30 cm at a speed of1,000 to 1,400 cm/sec (Paneth et al. Ber. 1929 62 1335). In order toobtain the necessary pressure in the radiation zone, while maintaining apredetermined NOCI concentration, the nitrosating agent may be conveyedby a gas vehicle, which may be inert, or may contribute to the reactionlike hydrochloric acid.

The radiation zone, in which the nitrosating agent undergoesphotochemical dissociation, may take various forms.

FIG. 1 shows a reactor made from an opaque, corrosion-resistant materialsuch as polyvinyl chloride, in which the radiation and dissociationzones consist of pipes 2, which have capillary ends or which areobstructed crosssectionally by a transparent screen made from Pyrex,quartz or fluorous resins. The lightradiation sources 3 are placedbetween these pipes. The cycloalkane, in liquid form or in solution, isinjected through one inlet 4, and the hydrochloric acid through another6, while a stirrer 5 ensures that the reaction mixture is homogeneous.The nitrosating agent 8, alone or carried by a vehicle consisting ofnitrogen, argon, anhydrous hydrochloric acid or carbon tetrachloride, isinjected and dissociated into activated particles in the pipes 2. Theseparticles are transferred quickly to the actual chemical reactor 1.

Another embodiment consists of placing the lightsources 3 directlyinside the pipes 2 carrying the nitrosating agent and its vehicle 8.

FIG. 2 shows a third embodiment, consisting of a reactor with a doublecasing. The outer casing 10 may be totally or partly transparent, whilethe inner casing 1 1, marking the boundary of the inner chemicalreaction zone 12, consists of a perforated, opaque, corrosionresistantmaterial 14. The energy sources 3 are placed outside the outer casing10, opposite the transparent sections, or between the two casings.

The nitrosating agent and its vehicle are fed into the space between thetwo casings 13, where radiation causes dissociation and/or activation,producing active particles of Cl* and NO*; these are carried by thevehicle through the perforations 14 into the reaction zone, wherecycloalkane is added through one pipe 4 and hydrochloric acid throughanother 6.

FIG. 3 shows a fourth embodiment, which is particularly recommended.This involves a perforated casing 15 surrounding each lamp 3. Thenitrosating agent, alone or diluted in a vehicle, is fed into the space16 between the lamp and the perforated casing, at sufficient pressure toprevent any of the reagents in the reaction zone 17 from leaking in. Theliquid or dissolved cycloalkane is fed into the reactor through one pipe4, and the hydrochloric acid through another 6. In this apparatus thenitrosyl chloride is dissociated by radiation in the space between thelamp and diffusion screen or perforated casing, and oximation occurs inthe actual reaction zone, after diffusion of the active particlesthrough the space between the casing and outer wall of the reactor.

The length of time the active particles remain in the radiation zonedepends on the pressure, the distance between the surface of the lampand the perforated casing, and the transparency of the casing.

The amount of transparency, or perforated area in relation to the totalsurface area of the casing, and the average diameter of theperforations, can also vary widely, reaching as much as 50 percent.

If T is the amount of transparency of the perforated casing, T percentof the light energy emitted may be assumed to pass into the reactionzone, where a secondary process is brought about by injecting enoughnitrosating agent to use it. The agent is thus injected simultaneouslyinto the annular space between light source and casing, and into thereaction zone, ensuring maximum utilization of the photon emitted by thelamp.

The yield is also increased because ClNO molecules that escape into thereaction zone before dissociation has occurred and C1 moleculesresulting from recombination of active chlorine ions can bere-dissociated by means of the light energy reaching the reaction zone,and react with the cycloalkane.

It has also been found that the field from some photochemical reactionsis better when the radiation source functions with alternating periodsof illumination and extinction in a zone adjoining the grid. Theperforated casing enables this alternation to be reproduced along thepath of the active particles.

Finally, the spectral distribution in the reaction zone is notnecessarily the same as in the space inside the perforated casing, sincethe shorter wavelengths tend to be absorbed before passing into thereaction zone, which thus receives longer wavelengths that are lessharmful to the oxime. Absorption in the radiation zone increases withthe concentration of nitrosating agent, and with the distance betweenlamp and casing.

The invention is illustrated by, without being confined to, thefollowing examples.

EXAMPLE 1 Description of the Apparatus FIG. 3 shows a reactor with aperforated inner casing, 15, cut away to reveal the lamp. Thiscylindrical casing in 47 mm in diameter and 1 10 mm high, and is made ofa corrosion-resistant material such as stainless steel, nickel,titanium, or any other suitable alloy. It may also be of sinteredaluminum or refractory material, or consist of a metal base coated witha fluoro carbon poly mer, or of an optically transparent fluoro carbonpolymer. The number of perforations varies from to 10,000 per square cm,and they may cover from 5 to 50 percent of the total surface-area of thecasing.

The use of electroformed nickel or alloy grids is particularlyrecommended. These have the advantage of reflecting all the photonsproduced, whereas hydrophobic coatings such as fluoro carbon polymersand silicones absorb them.

The cross-sectional area of the perforations may be of anygeometricalform. The casing 15 is held at the base in a machinedpolytetrafluorethylene support 18, attached by a system of machinedrings, joints and flanges 19, also made of fluoro carbon polymer.

The nitrosyl chloride 8, alone or mixed with a gas vehicle, is injectedinto the annular space between the lamp cover and the perforated casingthrough a pipe 20 and bent connection 21.

The energy source 3 is a 450 W high-pressure mercury lamp, 11 mm indiameter, mm long, with a cover 40 mm in diameter.

This unit is placed inside a reactor 17, 450 mm high and 110 mm indiameter.

To perform the process, the pressure in the space between the lightsource and perforated casing is raised by injecting a gas vehicle, toprevent any subsequent infiltration of the reaction mixture. When thepressure is high enough, nitrosyl chloride 8 is injected through thepipe 20, and the reaction mixture through another pipe 4, the amountbeing adjusted so as not to rise above the top of the perforated casing.The light source is switched on. Hydrochloric acid is added throughanother pipe 6, and the oxime hydrochloride that forms is extractedthrough the base of the reactor 22.

EXAMPLE 2 Cyclohexane is fed continuously into the reactor described inExample 1, using a perforated casing with 23 percent transparency.

16 litres of ClNO an hour circulate between the lamp cover and casing,in a gas vehicle such as anhydrous hydrochloric acid mixed withnitrogen, at a rate of l 1.5 litres an hour.

Liquid cyclohexane is fed into the reactor at a rate of g an hour,saturated with anhydrous hydrochloric acid, injected separately.

The reaction mixture is kept at a temperature of 15C.

The reactor produces 100 g of oxime an hour, and the reaction can beperformed continuously, without the lamp becoming dirty.

EXAMPLE 3 The process is repeated as in Example 2, using a perforatedcasing with 23 percent transparency, except that ClNO is simultaneouslyinjected into the reaction zone at a rate of 10 litres an hour, to useup the light energy reaching the reaction zone through the 23 percenttransparency.

The oxime output rises to 139 g an hour.

EXAMPLE 4 A 20 percent solution of cyclododecane in carbon tetrachlorideis injected at a rate of 300 g of cyclododecane an hour. The flow andpressure of ClNO and HCl are the same as for Example 2. 200 g of oximean hour are obtained.

EXAMPLE 5 The process is repeated as in Example 4, but using moltencyclododecane, which is injected at a rate of 300 g an hour. Thereaction temperature is between 65 and 70C. ClNO is simultaneouslyinjected into the reaction zone as in Example 3. The oxime output is 250g an hour.

What is claimed is:

l. A photochemical reactor comprising a first zone adapted to receive agaseous reagent and a second zone adapted to receive a liquid reactionmedium said zones being separated by a gas-permeable partition, andlight source associated with said first zone and out of contact withsaid second zone, whereby gaseous reagent is dissociated into activatedradicals in said first zone by said light source and said activatedradicals pass through said gas-permeable partition into said liquidreaction medium in said second zone.

2. The photochemical reactor of claim 1 wherein one of said zones ispositioned around the other of said zones.

3. The photochemical reactor of claim 2 wherein a first zone is an innerzone and a second zone is the outer zone separated from said inner zoneby a cylindrical gas-permeable partition, and said light source iscoaxially positioned within said inner zone.

4. The photochemical reactor of claim 3 wherein said inner zone includeselectrical connections for said light source and has an inlet pipe forsaid gaseous reagent.

5. The photochemical reactor of claim 3 having plurality of first zoneswithin said second zone, each of said first zones having a light sourcepositioned therein and each of said first zones being separated fromsaid second zone by a gas-permeable partition.

6. The photochemical reactor of claim 2 wherein said first zone is anouter zone by a cylindrical gaspermeable partition, and said lightsource is positioned outside said outer zone.

7. The photochemical reactor of claim 2 wherein said first zone is anouter zone and said second is an inner zone separated from said outerzone by a cylindrical gas-permeable membrane, and said light source ispositioned within said outer zone.

2. The photochemical reactor of claim 1 wherein one of said zones ispositioned around the other of said zones.
 3. The photochemical reactorof claim 2 wherein a first zone is an inner zone and a second zone isthe outer zone separated from said inner zone by a cylindricalgas-permeable partition, and said light source is coaxially positionedwithin said inner zone.
 4. The photochemical reactor of claim 3 whereinsaid inner zone includes electrical connections for said light sourceand has an inlet pipe for said gaseous reagent.
 5. The photochemicalreactor of claim 3 having plurality of first zones within said secondzOne, each of said first zones having a light source positioned thereinand each of said first zones being separated from said second zone by agas-permeable partition.
 6. The photochemical reactor of claim 2 whereinsaid first zone is an outer zone by a cylindrical gas-permeablepartition, and said light source is positioned outside said outer zone.7. The photochemical reactor of claim 2 wherein said first zone is anouter zone and said second is an inner zone separated from said outerzone by a cylindrical gas-permeable membrane, and said light source ispositioned within said outer zone.